200 PHOLADID.E. 



hour's constant observation under the lens, issued from the 

 anal siphon, a sufficient proof of the non-communication of 

 the two ; but as soon as the anal siphon was allowed to reach 

 the water and obtain a supply, the current recommenced. 



I now come to another experiment from which Messrs. 

 Alder and Hancock conclusively infer the connection of the 



w 



siphoiial currents. They state, " that the iiosle of a blowpipe 

 charged with a coloured fluid was placed at the inhalant orifice 

 of a Pholas, and immediately a quantity was drawn into the 

 animal. Watching carefully the result, we had soon the 

 satisfaction of beholding a blue-stained stream issue from the 

 exhalant orifice." 



To this I observe, that having tried the experiment again 

 and again, failure always occurred ; as the animal, after re- 

 ceiving the coloured fluid, which was applied without difficulty, 

 in general immediately discharged it by the pedal gape, or by 

 the branchial aperture overwhelming with coloured matter 

 both tubes, the orifices of which, from their inflection by the 

 animal, were so retracted and blended together as to be undis- 

 coverable ; of course, any issue of liquid from a particular tube 

 was undistiiiguishable. When, in any example, the fluid, 

 which was coloured by archil, remained a little time without 

 expulsion, I opened the branchial cavity to see if the gill- 

 laminse and interbranchial tubes showed anv increased infla- 



v 



tion or colour from the filtration of the injection, but no 

 unusual appearance presented itself. I also opened the anal 

 vault and collected with a camel's-hair brush as much of the 

 moisture as possible ; this was applied to a very small quantity 

 of distilled water, but no trace of colour appeared ; we may 

 then presume that none of the injection had passed from one 

 siphon to the other. But when the coloured fluid was ad- 

 ministered anally, all the interbranchial tubes were at once 

 filled and remained inflated more than an hour, representing 

 minute well-filled hoses, which bore the pressure of a delicate 

 wooden stylet, and exhibited the fluctuations of the liquid, 

 which, on its removal, instantly reverted to the points of dis- 

 placement, without any escape into the branchial chamber. 

 We may therefore conclude, that the interbranchial tubes are 



